In the case of optoelectronic semiconductor components, for example semiconductor lasers or LEDs, the service life of the component is correlated inter alia with the number of defects in the epitaxially grown semiconductor layers. The internal quantum efficiency is also reduced by a high number of defects, whereby the luminous efficiency is reduced. A high quality epitaxial growth substrate is required for the epitaxial growth of semiconductor layers with a low defect density.
In order to produce optoelectronic components based on nitride compound semiconductors, it is difficult to provide suitable epitaxial growth substrates which have a lattice constant suitable for the epitaxial growth of nitride compound semiconductors and which are simultaneously distinguished by a low defect density at their surface.
It is known to grow epitaxial semiconductor layers consisting of nitride compound semiconductors on SiC or sapphire substrates. However, when growing on such epitaxial growth substrates, a comparatively large amount of defects are produced at the interface between the epitaxial growth substrate and the epitaxial semiconductor layers, which defects extend from the epitaxial growth substrate through the component and are thus referred to as “threading dislocations”. The defects typically have a surface density (threading dislocation density (TDD)) of typically more than 108 cm−2.
Meanwhile, although substrates consisting of GaN having a comparatively low defect density of typically more than 105 cm−2 are available for the epitaxial growth of nitride compound semiconductors, the high price of such GaN substrates impede the commercial use in the mass production of optoelectronic components based on nitride compound semiconductors.
A further disadvantage in the use of GaN substrates resides in the fact that the epitaxial layers of the optoelectronic component cannot be readily separated from the epitaxial growth substrate in order to produce so-called thin-film components. Such thin-film components can be produced on a sapphire substrate after the growth of the epitaxial layer sequence for example by means of a laser lift off process. In the laser lift off process, laser radiation is radiated through the transparent epitaxial growth substrate and is absorbed at the interface between the epitaxial growth substrate and the epitaxial layer sequence, wherein the absorption of the laser radiation produces material decomposition at the interface which results in the separation of the epitaxial growth substrate. Such a laser lift off method is known for example from publication WO 98/14986. However, in contrast to substrates consisting of sapphire, generally this method cannot readily be applied to substrates consisting of GaN since the GaN epitaxial growth substrate is not transparent.